1. Field of the Invention
This invention generally relates to a video signal reproducing apparatus and more particularly to an apparatus arranged to reproduce video signals from a record bearing medium on which many tracks are formed in parallel to each other with a video signal for a given period of time recorded in each of the tracks and to perform reproduction using a memory device which is capable of storing the video signal for the given period.
2. Description of the Related Art
For adequately carrying out a so-called special reproduction such as slow-motion reproduction, a high speed search or look-up reproduction, etc. with a video tape recorder (hereinafter referred to as VTR for short), it has been proposed and practiced to arrange a head in addition to the normal recording and reproducing heads and to use it solely for the special reproduction.
However, this method increases the number of heads to make the arrangement of a rotary head drum complex and thus necessities a greater number of rotary transmitters for signal exchange with the heads mounted on the rotary drum. In the event of a rotary drum of small diameter, therefore, it becomes extremely difficult to mount and arrange the increased number of heads on the small drum. Besides, the rotary transmitters for these heads must be narrowly spaced thus running the hazard of the adverse effect of cross-talks among the rotary transmitters. In that instance, therefore, it is hardly possible to obtain an adequately reproduced video signal.
To solve this problem, a VTR which has recently been proposed is arranged to use a so-called field memory which has a storage capacity corresponding to one field portion of a video signal; to write into the memory only some acceptable parts of a reproduced video signal obtained from the normal reproducing head; and thus to always adequately carry out a special reproducing operation by reading out the good video signal parts from the field memory. This VTR is capable of adequately carrying out the special reproduction without increasing the number of heads.
This method of carrying out the above stated special reproduction by using a field memory, however, raises a question as to how to determine "the good parts of the reproduced video signal." This determination may be made in varied ways. For example, in one conceivable way, the reproduced signal may be determined to be good if the level of the reproduced RF signal thereof is higher than a given level. In another way, the reproduced signal may be determined to be good if not much tracking error is detected from the signal reproduced by the rotary head. The details of these methods are described in U.S. patent application Ser. Nos. 058,326, filed June 4, 1987 and 062,929, filed June 16, 1987, both of which having been assigned to the assignee of the present invention. Meanwhile, in the case of a VTR of the kind arranged to permit setting recording tracks at different track pitches, adoption of the above stated method presents the following problem:
The level of the reproduced RF signal and that of the tracking error signal to be used as criteria for determining the above stated "good reproduced video signal" are dependent on such parameters as the pitch and width of the recording tracks and the width of the head. With the "good reproduced video signal" thus determined by comparison with the given level, the generation frequency of the "good reproduced video signal" comes to vary with the pitch at which the recording tracks are formed.
If the criterion for determining the "good reproduced video signal" is set at a relatively high value, in case that a high speed search reproducing operation is performed, for example, for some of the recording tracks that have a low generation frequency of the "good reproduced video signal," the amount of the video signal written into the field memory comes to decrease. In this case, it is hardly possible to obtain output pictures in an adequate state either because the output time intervals of the reproduced pictures would become too long or because there might arise an unvarying part within the reproduced picture output.
Meanwhile, if the criterion for determining the "good reproduced video signal" is set at a low value, a high speed search reproducing operation, for example, on recording tracks having a low generation frequency of the "good reproduced video signal" would result in a deteriorated S/N ratio of the reproduced picture output, because: In that case, the reproduced video signal would be written into the field memory in a state of having an excessively poor S/N ratio.